1. Technical Field of the Invention
The present invention relates to a corrugated fin fixed onto an outer surface of a tube of a heat exchanger. More particularly, the present invention relates to a corrugated fin, on the surface of which a large number of louvers are formed.
2. Description of the Related Art
Conventionally, in order to increase a heat transfer area of a heat exchanger, the top and bottom portions of a corrugated fin are joined onto an outer surface of a flat tube in which a heat transfer medium flows. This corrugated fin is composed in such a manner that a thin metallic strip made of aluminum is bent into a wave-shape and a large number of louvers (sloping slats) are formed on the surface of the wave-shaped metallic strip.
The above corrugated fin is continuously formed when a metallic strip is supplied to a pair of forming-rollers. In the pair of forming-rollers, as a cutting edge for raising a large number of louvers, a large number of disk-shaped edges, on both sides of which edges are provided, are laminated together, and edges, on the one side of which an edge is provided, are arranged on both sides. Both-side-edges of a pair of forming-rollers form both-side-cut-louvers, and one-side-edges form one-side-cut-louvers.
However, although an inclination angle of the one-side-edge for forming the one-side-cut-louver J7 is the same as an inclination angle of the inclined face of both-side-edge, as shown in FIG. 13, the inclination angle of the one-side-cut-louver J7 after forming is smaller than the inclination angle of the both-side-cut-louver J8. The reason is that an amount of spring-back after forming of the corrugated fin of the both-side-cut-louver J8 and an amount of spring-back after the forming of the corrugated fin of the one-side-cut-louver J7 are different.
Due to the foregoing, a volume of air flowing in the opening portion of the one-side-cut-louver J7 becomes smaller than a volume of air flowing in the other both-side-cut-louver J8. Further, the air flowing angles are different from each other. Accordingly, the air current loses balance. Therefore, the heat exchange performance is deteriorated in the neighborhood of the one-side-cut-louver J7.
In order to solve the above problems, the following corrugated fin is proposed in the official gazette of JP-A-2002-205122. When a shape of the one-side-edge is changed, the spring-back of the one-side-cut louver is seldom caused, and the inclination angle of one-side-cut-louver and the inclination angle of the both-side-cut-louver are made to be the same.
However, in the corrugated fin described in the official gazette of JP-A-2002-205122, the shape of the one-side-edge is made to be a special shape different from the shape of the other edge. Therefore the manufacturing cost of the rollers for forming the corrugated fin is increased. Further, the forming property for forming the corrugated fin is deteriorated.